Pole piece mounting structure in crt convergence electrode



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J. H. JOHNSON Dec. 2, 1969 POLE PIECE MOUNTING STRUCTURE IN CRT CONVERGENCE ELECTRODE Filed Jan. 5, 1969 INVENT OR JAY H. JOHNSON ATTORNEY United States Patent U.S. Cl. 31385 4 Claims ABSTRACT OF THE DISCLOSURE A three-gun color picture tube convergence cup is formed with only three wide slots in its cylindrical side walls. Each slot has two opposite edges forming a gauge against which two magnetic pole pieces for each electron beam are precisely located into a critical position to influence the electron beams.

This invention relates to the structure of electrodes in cathode ray tubes and more particularly to the mounting structure for magnetic convergence pole pieces in a convergence cup electrode.

At the present stage of development of three gun picture tubes a convergence cup electrode assembly is positioned inside the neck of a cathode ray tube to process three electron beams individually by means of external electromagnetic dynamic convergence means about the tube neck. This art of controlling convergence of electron beams magnetically within the electron gun of color picture tubes is extremely critical and depends to a large extent to critical dimensions and structural relationships of the convergence cup electrode assembly. It has been customary in prior art for each beam to use two generally L-shaped magnetic pole pieces extending through individual narrow axial slits located below the open rim of cylindrical convergence cup walls. The pole pieces are disposed in a substantially radial direction through the slits to span the axial beam path through the electrode.

This customary construction has led to several problems. Since the cup body and side walls are cylindrical and are formed of hard non-magnetic metal such as stainless steel, it has been difiicult to punch thin slits in the walls in a precisely located position. As a thin punch member strikes the cylindrical surface it tends to be deflected out of position and worn quickly to cause considerable variation in slit size and position. Thus, it is difficult to exactly locate the slit as precisely as necessary to use for positioning a magnetic pole piece closely adjacent the electron beam path. Also the necessity to position a pole piece through a narrow slit requires a tedious needle-threading procedure in construction adding to the cost and possibly causing rejects because of scratches or distortions incurred in positioning.

Furthermore the six separately punched thin slits required about the cup walls for insertion of six pole pieces tend to cause the walls to be bent and distorted from their critical roundness specifications, particularly if two or more punched holes are made simultaneously. In a color gun convergence assembly the pole piece spacing is closely adjacent the electron beam and thus becomes very critical in alignment because the magnetic effect varies as the square of the distance. Thus any slight mis-alignments are exaggerated in effect and frequently cause rejects. In a color picture tube it is critical that the operating conditions are established uniformly and identically on all three beams and thus any cylinder out of roundness," misplaced or distorted slots or misaligned pole pieces, and possible non-uniformity about the electrode cup circumference encountered in the customary prior art construction has "ice not been fully satisfactory. This invention seeks to correct the foregoing deficiencies by introducing novel structural changes which assure more precise construction within closer tolerances while at the same time reducing the construction cost.

It is therefore an object of this invention to provide improved convergence cup electrodes for cathode ray color picture tubes.

Another object of the invention is to provide convergence cup structure which can be precisely manufactured to critical tolerances at low cost.

Another object of the invention is to provide magnetic convergence cup electrode structure operating precisely and accurately upon three electron beams of a color picture tube to control dynamic convergence.

Therefore, in accordance with this invention the structure of the convergence cup electrode is changed to provide for only three slits in the circumferential walls, which are wide and have precisely positioned opposite edges serving as a jig or gauge for exactly locating two magnetic convergence pole pieces in the same slit to span the eletron beam of each gun.

A preferred embodiment of the invention is illustrated in the accompanying drawing, wherein,

FIGURE 1 is a perspective view of a convergence cup electrode assembly embodying the invention and FIG- URES 2 and 3 are respectively elevation and plan views of the convergence cup assembly.

It may be seen that the convergence electrode assembly comprises a hollow cylindrical thin-walled cup body 5 of non-magnetic material such as stainless steel with a closed bottom 6 having three apertures 7, 8, 9 through which the three respective electron beams pass axially through the cylindrical cup body. The top of the cup body 5 is open. Magnetic shield means 10 are contained fully within the cup body and afiixed to its circumferential side walls by means of flanges 11 conforming with the inner wall of the cup body. The shield means 10 divides the cup into three compartments 12, 13, 14 extending about the apertures 7, 8, 9 and alongathe axial path of the beam through the cup.

In the cup walls are disposed three wide slots 15, 16, 17 ranging from near the bottom 6 through the top rim 22 of the cup respectively within each compartment 12, 13, 14. Each slot has opposite edges 18, 19 against which are registered in precise position a pair of magnetic pole pieces 20, 21, which comprise generally L-shaped members having one arm conformed against and affixed to the outer cylindrical cup body wall and extending circumferentially away from the slots 15, etc.

Each pole piece is similar to those used in prior art construction having an inner leg 23 disposed generally radially into the interior of the cup body to have a plate portion lying closely adjacent the axial beam path through the electrode. This plate portion may be conformed in shape to include such structure as semi-cylindrical indentations along the axial beam path if desired.

It may be seen from this construction that a wide die that is not readily deflected and thus stays sharp and precisely in position even when encountering a hard cylindrical surface, is used to form slots 15, 16 and 17 and precisely locate edges 18, 19 for abutment against the apex of pole pieces 20 and 21, etc. thereby accurately positioning each pole piece. The open topped wide slots 15, etc. present no problem of registration or entry of the pole pieces such as when presented through narrow or restricted area slots of the prior art and can be done either manually or automatically with machinery. No ambiguity is left in the precise positioning of the pole pieces as would occur if the cup body slot edges 18, 19 or some similar structure were not used for or were not accurately enough located for referencing the position of the pole pieces. Furthermore the pole pieces can readily be held against the edge so they cannot slip or move during a spot welding operation.

By putting the shield means 10 completely inside the cup no other small slits or slots are necessary in the cup and any tendency thereby to lose roundness is limited. The snubber springs 25, 26, 27 are affixed to the outer cylindrical wall at a position spaced from the pole pieces 20 and 21 to center the convergence assembly within the neck of the tube body (not shown). Thus the entire assembly provides a combination of structural features which work together to achieve the critical function of dynamically converging the three electron beams of a color picture tube.

It is seen therefore from the described embodiment that a convergence cup assembly having the novel structure set forth with only three wide slots in its circumferential walls will afford closer tolerances at lower construction costs, and therefore provide improved more efiicient operation in the processing of a color picture tube electron beam.

What is claimed is:

1. A convergence electrode assembly for mounting in the neck portion of a three-beam color television tube to process a plurality of electron beam directed through the assembly, comprising in combination, a hollow cylindrical thin-walled electrode cup body of non-rnagnetic material having a closed bottom with three apertures through which three electron beams are passed axially through the cup body and having a generally open top, shield means of magnetic material dividing the cup body into three compartments extending about said apertures and the axial path of the electron beams through the cup body, said shield means extending to the cup walls at spaced positions about the circumference and being affixed to the cup body, three wide aperture slots in the circumferential walls of the cup body within the respective compartments defined by said shield means disposed to extend substantially the entire axial length of the cup body and to present two opposite edges aligned axially at positions circumferentially spaced to define segmental openings in the cup body walls, and a pair of magnetic pole pieces aligned in each said wide slot at the opposite edges to extend substantially radially into the cup body on opposite sides of the axial beam path through the cup body.

2. A convergence cup assembly as defined in claim 1 wherein the pole pieces comprise substantially L-shaped members having one arm conformed against and aflixed to the outer cylindrical cup body wall in a circumferential direction away from the edge of the slot.

3. A convergence cup assembly as defined in claim 1 wherein said slots extend to the open top rim of said cup body.

4. A convergence cup assembly as defined in claim 2 wherein the cup side walls have only said three slots therein, including a set of three snubber springs for positioning the cup assembly within the neck of the tube, each respectively aflixed to the outside wall of the cup body at a position spaced from the pole pieces, and a mounting flange on said shield means conforming to the inner wall of said cup body and affixed thereto to be confined wholly within said cup body.

No references cited.

JAMES W. LAWRENCE, Primary Examiner V. LAFRANCHI, Assistant Examiner US. Cl. X.R. 3l377 

